Deterministic EMI grid layout for controlling optical diffraction
An electromagnetic interference shield is disclosed. The electromagnetic interference shield includes an optically transparent substrate and a metallic coating on the optically transparent substrate. The metal coating is characterized by a plurality of apertures aligned in a pattern that is defined by a deterministic relation. Distances between each of the plurality of apertures and an observation point in an associated image plane are uncorrelated.
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The present disclosure relates to a metallic shield for reducing electromagnetic interference (EMI), and more specifically, to a metallic grid that additionally reduces diffractive effects at optical wavelengths.
Electromagnetic interference (EMI) is a disturbance to an electrical circuit due to electromagnetic radiation emitted from an external source. Protecting a circuit from EMI generally involves placing a metallic grid between the circuit and the external source. The metallic grid generally consists of a patterned metal coating applied to an optical substrate. In addition to protecting against EMI, the patterned metal coating is designed to allow transmission of optical wavelengths through the coating. In various implementations of a patterned EMI-reducing coating, the presence of the coating unavoidably reduces optical transmission, both by blocking light and by diffracting a portion of the transmitted light, resulting in signal loss and increased background illumination. In various applications, it may be useful to pass light (i.e., a designator beam) from a light source such as a laser through the metallic grid to identify an object. However, if the pattern of the grid is periodic, light passing through the grid may generate a diffractive scatter halo having side lobes, which are bright peaks of light appearing in the diffractive halo surrounding the desired (specular) beam. Additionally, the side lobes may fall on objects other than a target that is to be identified, giving rise to the possibility of a false positive identification. Therefore, there is a need to reduce the diffractive effects at optical wavelengths.
According to one embodiment of the present disclosure, an electromagnetic interference shield includes an optically transparent substrate; a metallic coating on the optically transparent substrate, the metal coating characterized by a plurality of apertures aligned in a pattern that is defined by a deterministic relation, wherein distances between each of the plurality of apertures and an observation point in an associated image plane are uncorrelated.
According to another embodiment, a method of shielding an object from an electromagnetic signal includes: forming a metallic coating characterized by a plurality of apertures aligned in a pattern that is defined by a deterministic relation, wherein distances between each of the plurality of apertures and an observation point in an associated image plane are uncorrelated; and placing the metallic coating between the object and the electromagnetic signal.
According to another embodiment, a method of reducing diffraction effects in an electromagnetic interference shield, comprising: forming the electromagnetic interference shield using a metallic coating having a plurality of apertures aligned in a pattern that is defined by a deterministic relation, wherein distances between each of the plurality of apertures and an observation point in an associated image plane are uncorrelated.
Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure. For a better understanding of the disclosure with the advantages and the features, refer to the description and to the drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The subject matter which is regarded as the disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Squares 414 and 416 are shown to illustrate a granular metal density of a coating having the aperture pattern 400. The granular metal density is related to a local conductivity of the coating. This local conductivity varies across the grid as a result of the random placement of apertures 401 in pattern 400. For a selected square, a granular metal density may be determined by measuring the lengths of the sum of aperture segments within in a selected square. Square 414 and square 416 have the same dimensions. It is clear that the metal density in square 414 is less than the metal density in square 416. This difference in metal density is evident in the relative semi-transparency of the grid in square 414 in comparison to the relative opacity of the grid in square 416. In fact, the granular metal density is unevenly distributed over the pattern 400. Thus, the electrical conductivity or the ability of the random pattern 400 to shield circuitry from electromagnetic pulses is weaker in the area defined by square 414 than it is in the area defined by square 416. Thus, random placement of the apertures produces a metallic coating that, although reducing the presence of side lobes in image 500, has potentially uneven EMI shielding abilities.
s=a+bθ Eq. (1)
where s is the spiral curve 603, a is an angular offset of the pattern 600 of the spiral 603, b is a scalar dimension of the spiral equal to the distance between the turns of the spiral 603 and θ is the angle parameter of the spiral 603. These pattern parameters of Eq. (1) can be selected by a designer to fit a selected criterion or multiple selected criteria. In an exemplary embodiment, circles 601, which form apertures of the pattern 600, are placed in the Archimedes spiral 603. A first circle is placed in the spiral starting at a place nearest the origin 620 of the spiral 603. Each subsequent circle is placed in the spiral 602 adjacent the previous circle so that the boundaries of the circles make contact at a substantially single point, i.e., the boundaries of the circles are in contact without overlapping of the circles. A selected circle is in contact with the spiral 603 at two substantially diametrically opposed locations. This process of adding apertures may be continued to produce the exemplary pattern 600. The pattern 600 formed from using this deterministic method has neither translational symmetry nor rotational symmetry. Additionally, the phase relation between the circles 601 are uncorrelated, leading to an uncorrelated phase relation at side lobes of the image, as discussed below.
In the exemplary pattern 600, various elements are shown that are not part of the pattern 600 when the coating is manufactured, but which are shown for explanatory purposes to discuss various aspect of the pattern 600. These explanatory elements include the vertical line 610, the shading of selected apertures 612, and the square areas 614 and 616. The vertical line 610 and shaded apertures 612 illustrate the random or uncorrelated relation of the apertures. The apertures fall along a non-periodic “lattice.” Additionally, each aperture is separated by a distance from an observation point in an associated image plane. The plurality of these distances associated with the plurality of apertures within the pattern is uncorrelated. The perpendicular distances between the centers of the shaded apertures 612 and the vertical line 610 are uncorrelated although there placement is a result of a deterministic placement method rather than a random placement method. As a result, the phase relation of light are uncorrelated at the side lobes in the image plane (see image plane 700 of
In alternate embodiment of the present disclosure, the pattern 600 may include a second spiral that passes through the centers of the circles 601. In another embodiment, the spiral 603 may be filled with half-circles. The half-circle embodiment may be suitable to allow simple adjustments of surface resistance of the metal coating by changing a spacing between the semicircles. The embodiment using semi-circles allows for adjustments of a halo irradiance by scaling the entire pattern, while maintaining resistivity by scaling the relative half-circle spacing along the spiral. In another embodiment, the spiral connecting the edges of the circles may be dispensed with by using circles that are larger in diameter than the spacing of the individual turns of the spiral (‘b’ of Equation 1), thereby causing the circles to overlap those in adjacent turns of the spiral. In other embodiments, the shape of the aperture may be non-circular, i.e., elliptical, polygonal, etc. While the Archimedes spiral 603 is used as an illustrative example, any algebraically deterministic curve that organizes apertures in a pattern wherein the distance of each of the apertures to any given point in the associated image space is random or uncorrelated may be used in other embodiments of the disclosure.
In other aspects of the present disclosure, the use of an algebraically deterministic coating pattern allows a designer to change one or more parameters of the grid pattern to increase or decrease the ability of the resultant coating to protect from EMI, while maintaining the ability of the resultant coating to reduce the appearance of side lobes in an image plane. Changing the ability of the coating to protect from EMI requires changing the electrical resistance of the grid, which requires changing the relative area of the substrate being covered by the grid pattern. For example, if the overall pattern is scaled by changing the value of ‘b’ in Equation 1, but the width of the metal lines making up the pattern are not scaled, then the relative area covered by the pattern will change by that overall scale factor. The fractional area covered by the pattern represents a blocking obscuration to incident optical light. Thus, the designer may design a pattern that trades off EMI protection for optical transmittance, while maintaining side lobe reduction. In addition, a manufacture of the coating may be controlled by selection of pattern parameters, thereby streamlining the manufacturing process. By naming the value of the width of the metal line, the diameter of the circle (aperture), the value of ‘b’ in Equation 1, and the location of the spiral origin on the optical substrate, the entire grid pattern may be specified for the manufacturing process, and its expected performance may be determined, both in terms of EMI performance and optical performance.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated
While the exemplary embodiment to the disclosure has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the disclosure first described.
1. An electromagnetic interference shield, comprising:
- an optically transparent substrate; and
- a metallic coating on the optically transparent substrate, the metal coating characterized by a plurality of apertures aligned in a pattern, wherein the pattern has neither translational symmetry nor rotational symmetry and the granular metal density in each square area on the metallic coating is substantially the same,
- wherein the pattern is formed as an Archimedes spiral of the plurality of apertures.
2. The electromagnetic interference shield of claim 1, wherein a parameter of the pattern is selected to control at least one of: (i) an electrical property of the metallic coating; and (ii) an optical property of the metallic coating.
3. The electromagnetic interference shield of claim 1, wherein the alignment of the plurality of apertures in the pattern provides a substantially uniform average distribution of metal in the metallic coating.
4. The electromagnetic interference shield of claim 1, wherein the pattern of the plurality of apertures in the metallic coating produces an uncorrelated phase relation of light, diffracted upon passing through the metal coating, at an image plane of the metallic coating.
5. The electromagnetic interference shield of claim 4, wherein the uncorrelated phase relation reduces an appearance of side lobes at the image plane.
6. The electromagnetic interference shield of claim 1, wherein the apertures forming the Archimedes spiral are circular.
7. The electromagnetic interference shield of claim 6, wherein a parameter of the pattern includes a parameter of the spiral or a thickness of the plurality of apertures.
8. The electromagnetic interference shield of claim 1, wherein adjacent apertures are at least one of non-overlapping and contacting each other at their boundaries.
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Filed: Dec 6, 2012
Date of Patent: Jan 2, 2018
Patent Publication Number: 20140158417
Assignee: GOODRICH CORPORATION (Charlotte, NC)
Inventors: William Paul Zmek (Bethlehem, CT), Steven Sumner Prince (Bethlehem, CT)
Primary Examiner: Hung V Ngo
Application Number: 13/706,689
International Classification: H05K 9/00 (20060101);